Method and power transmitter for controlling power transmission

ABSTRACT

Methods and apparatuses are provided for method is provided for controlling power transmission in a power transmitter. Voltage information required by a plurality of power receivers is received from the plurality of power receivers. The voltage information includes a minimum voltage, a reference voltage that is greater than the minimum voltage, and a demanded voltage. Power is transmitted to the plurality of power receivers. A report about a power reception condition while transmitting the power is received from the plurality of power receivers. The report includes a measured voltage at the plurality of power receivers. One of the plurality of power receivers is selected. An amount of the power is adjusted by minimizing a difference between the demanded voltage and the measured voltage of the selected power receiver.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 13/896,931, filed in the U.S. Patent and TrademarkOffice on May 17, 2013, which claims priority under 35 U.S.C. § 119(a)to Korean Patent Applications filed in the Korean Intellectual PropertyOffice on Jul. 10, 2012 and Jul. 30, 2012, and assigned Serial Nos.10-2012-0075274 and 10-2012-0083546, respectively, the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a wireless power transmissionsystem, and more particularly, to a method for controlling power of apower transmission transmitter.

2. Description of the Related Art

Wireless and contactless charging technologies have recently beendeveloped and applied to many different electronic devices. The wirelesscharging technology, which uses wireless power transmission andreception, enables, for example, a battery of a cell phone to beautomatically charged by placing the cell phone on a charging pad. Thewireless charging technology does not require a separate chargingconnector. The wireless charging technology wirelessly chargeselectronic products and eliminates the need for a wired charger, therebycontributing to an electronic product's ability to be waterproof andportable.

In resonance method based charging, when a power receiver in need ofcharging is located in a power transmitter for transmitting wirelesspower, the power transmitter may charge the power receiver. If aplurality of power receivers is placed in a charging area of a singlepower transmitter, the power demanded from each power receiver may bedifferent from the transmission power of the single power transmitter.Thus, charging for each power receiver needs to be conductedefficiently.

A conventional power transmitter establishes a voltage reference forpower control to efficiently supply power to the power receiver.However, charging efficiency may vary depending on various chargingconditions, such as, for example, characteristics of the power receiver,hardware design, a distance between the power receiver and the powertransmitter, a charging position, etc.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present inventionprovides an apparatus and method for conducting efficient powertransmission in a power transmitter.

Another aspect of the present invention provides an apparatus and methodfor determining power demanded from a power receiver.

In accordance with an aspect of the present invention, a method isprovided for controlling power transmission in a power transmitter.Voltage information required by a plurality of power receivers isreceived from the plurality of power receivers. The voltage informationincludes a minimum voltage, a reference voltage that is greater than theminimum voltage, and a demanded voltage. Power is transmitted to theplurality of power receivers. A report about a power reception conditionwhile transmitting the power is received from the plurality of powerreceivers. The report includes a measured voltage at the plurality ofpower receivers. One of the plurality of power receivers is selected. Anamount of the power is adjusted by minimizing a difference between thedemanded voltage and the measured voltage of the selected powerreceiver.

In accordance with another aspect of the present invention, a powertransmitter is provided for controlling power transmission. The powertransmitter includes a resonator and a power supply. The powertransmitter also includes a wireless communication unit configured toreceive, from a plurality of power receivers, voltage informationrequired by the plurality of power receivers, where the voltageinformation includes a minimum voltage, a reference voltage that isgreater than the minimum voltage, and a demanded voltage, and toreceive, from the plurality of power receivers, a report about a powerreception condition while transmitting power, where the report includesa measured voltage at the plurality of power receivers. The powertransmitter further includes a controller configured to control thepower supply to transmit the power to the plurality of power receiversthrough the resonator, select one of the plurality of power receivers,and adjust an amount of the power by minimizing a difference between thedemanded voltage and the measured voltage of the selected powerreceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a power transmitter and a powerreceiver, according to an embodiment of the present invention;

FIG. 2 is a graph illustrating setting ranges of input voltages,according to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating a reference voltage establishmentmethodology in the power receiver, according to an embodiment of thepresent invention;

FIG. 4 is a flowchart illustrating a reference voltage and demandedvoltage establishment methodology in the power receiver, according toanother embodiment of the present invention;

FIG. 5 is a diagram illustrating signal transmission and receptionbetween the power transmitter and the power receiver, according to anembodiment of the present invention;

FIG. 6 is a graph illustrating power control methods, according to anembodiment of the present invention; and

FIG. 7 is a diagram illustrating a method of classifying power controlmethods, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described in detail withreference to the accompanying drawings. The same or similar componentsmay be designated by the same or similar reference numerals althoughthey are illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present invention.

Embodiments of the present invention propose a method of controllingefficient power transmission in a power transmitter. In an embodiment ofthe present invention, a power receiver notifies the power transmitterof minimum and maximum voltages that may be received at the powerreceiver, a reference voltage that acts as a reference for determining aregion having good charging efficiency, and a demanded voltage at thepower receiver. The power transmitter determines a best efficientvoltage region having good efficiency based on the reference voltage,and adjusts the transmission power according to a power receivingcondition received from the power receiver, which is being powered bythe transmission power. Accordingly, efficient power control isaccomplished by adaptively adjusting the transmission power based on thepower receiving condition to guarantee the best charging efficiency inthe power receiver.

The demanded voltage and the reference voltage are described in greaterdetail below. When the power receiver receives power from the powertransmitter, there is an input voltage Vin having the best chargingefficiency. However, in the power receiver, a desired optimum inputvoltage Vin having the best charging efficiency varies depending onvarious circumstances, such as, for example, hardware designs, chargingconditions, temperatures, etc. Therefore, when power transmission isconducted using only the minimum and maximum voltages in the powertransmitter, the transmission power is determined to be within a rangebetween the minimum and maximum voltages. However, since the rangebetween the minimum and maximum voltages is too wide to determine thetransmission power therein, the charging efficiency in the powerreceiver may vary significantly within the range. Thus, if it ispossible to determine a portion of the range between the minimum andmaximum voltages having the best charging efficiency for the powerreceiver, more efficient power transmission would be accomplished.

Embodiments of the present invention propose a method of determining arange having the best charging efficiency from within the range betweenthe minimum and maximum voltages. In the following description, avoltage to be used for determining the range having the best chargingefficiency, i.e., a power reception efficiency greater than a certainefficiency, is defined as a reference voltage V_high, and an optimuminput voltage Vin required by the power receiver is defined as ademanded voltage V_opt. Specifically, the reference voltage is a voltagethat is used to divide the range between the minimum and maximumvoltages into predetermined portions. A range between the referencevoltage and the minimum voltage has a relatively high power receptionefficiency when compared with other ranges.

A method of determining the reference voltage and the demanded voltagein the power receiver is described in greater detail with reference toFIG. 1. FIG. 1 is a block diagram illustrating a power transmitter 100and a power receiver 110 constituting a wireless power transmissionsystem, according to an embodiment of the present invention. In FIG. 1,the power transmitter 100 and the power receiver 110 are shown to beconnected in one-to-one relationship, however, the wireless powertransmission system of embodiments of the present invention may alsoinclude one or more power transmitters 100 and one or more powerreceivers 110. The power receiver may be embodied as, for example, acell phone, a Personal Digital Assistant (PDA), a Moving Picture ExpertsGroup (MPEG)-1 or MPEG-2 Audio Layer III (MP3) device, a laptopcomputer, a camera, or any kind of electronic device.

Referring to FIG. 1, the power transmitter 100 is configured to includea power supply 10 having, e.g., a Voltage Control Oscillator (VCO) forsupplying power to generate a resonant frequency signal determined by acontroller 18. The power transmitter 100 also includes an amplifier 12for amplifying the signal generated by the power supply 10 according tothe power supplied from the power supply 10. The power transmitter 100additionally includes a resonant signal generator 14 for transmittingthe power from the power supply 10 in a wireless resonant signal,according to the high-amplitude signal generated by the amplifier 12.The power transmitter 100 further includes a voltage/current measuringunit 16 for measuring the voltage and current generated by the powersupply 10, and the controller 18 for controlling general wireless powertransmission operations of the power transmitter 100. In particular, thecontroller 18 monitors a voltage and a current of the wirelesslytransmitted resonant signal according to the voltage and currentdetected at the voltage/current measuring unit 16, and controlsoperations of the power supply 10 and amplifier 12 to maintain thevoltage and current of the resonant signal to be in a preset normalrange. The power transmitter 100 also includes a wireless communicationunit 19 configured to employ one of a variety of wireless short rangecommunication schemes, such as, for example, Bluetooth, to communicatewith the power receiver 110 in relation to the operations of thewireless power transmission under control of the controller 18. Theresonant signal generator 14 includes a charging substrate, on which toposition the power receiver 110, in an upper part of the resonant signalgenerator 14.

The controller 18 of the power transmitter 100 may be configured with,e.g., a Micro Controller Unit (MCU), which controls the powertransmission by determining a range having the best charging efficiencyfor each of one or more power receivers, as described in greater detailbelow.

The power receiver 110 includes a resonator 20 for receiving thewireless resonant signal transmitted from the resonant signal generator14 of the power transmitter 100. The power receiver 110 also includes arectifier 22 for rectifying the power received via a matching circuit 21in an Alternate Current (AC) 21 to be in a Direct Current (DC) form. Thepower receiver 110 additionally includes a DC/DC converter 23 (alsoreferred to as a constant voltage generator) for converting poweroutputted from the rectifier 22 into an operating power (e.g., +5V)demanded by, e.g., a portable terminal established with such a powerreceiver. The power receiver 110 further includes a charger/PowerManagement Integrated Circuit (PMIC) 24 for being charged with theoperating power, and a controller 25 for measuring a voltage Vrectoutputted from the rectifier 22, i.e., an input voltage Vin, an outputvoltage Vout, and an output current Tout from the DC/DC converter 23.The controller 25 may be configured with an MCU, and determines a powerreceiving condition based on the measured voltage/current informationand provides information about the power receiving condition.

Specifically, the controller 25 of the power receiver 110 may change thereference voltage V_high, according to the voltage/current informationmeasured by the controller 25. Specifically, the reference voltageV_high may be changed based on the input voltage Vin, the output voltageVout, and the output current Tout. For example, the power receiver 110determines the reference voltage V_high to be 7 V, and notifies thepower transmitter 100 of the 7 V of the reference voltage V_high. If theoutput voltage Vout is measured to be 4 V during the charge, the powerreceiver 110 changes the reference voltage V_high to be 8 V. Thereference voltage V_high is changed because the power receiver 110determines that the current voltage output Vout is not enough forcharging, since the power receiver 110 knows in advance that the outputvoltage Vout may be 5 v±5% in normal charging. If the reference voltageV_high is 7 V, and the output voltage Vout, the output current Tout, andthe input voltage Vin are measured to be 5 V, 100 mA, and 6 V,respectively, the controller 25 of the power receiver 110 may determinethat input power exceeds the power that is required for charging, andmay change the reference voltage V_high to be 6 V. The controller 25 mayalso change the demanded voltage V_opt in addition to the referencevoltage V_high.

The power receiver 110 further include a wireless communication unit 26to communicate with the power transmitter 100 in relation to wirelesspower reception operations under control of the controller 25. Thewireless communication unit 26 operates by adopting one of a variety ofshort range wireless communication schemes. The wireless communicationunit 26 may transmit and receive various information and messagesrequired in the wireless charging procedure through the short rangewireless communication under control of the controller 25.

In an embodiment of the present invention, the wireless communicationunit 19 of the power transmitter 100 receives, from at least one powerreceiver, minimum and maximum voltages that the power receiver mayreceive, the reference voltage used for dividing the range between theminimum and maximum voltages into predetermined portions, and thedemanded voltage required by the power receiver, in a registrationphase, under control of the controller 18. The wireless communicationunit 19 of the power transmitter 100 also receives a report about thepower receiving condition, including a measured voltage at the powerreceiver 110 during power transmission from the power transmitter 100.The controller 18 determines whether the measured voltage is within therange between the minimum voltage and the reference voltage. If themeasured voltage is out of the range between the minimum voltage and thereference voltage, the controller 18 adjusts the transmission power.

When there is a plurality of power receivers in a charging area, in anembodiment of the present invention, the controller 18 receives minimumand maximum voltages and demanded voltages from the plurality of powerreceivers. The controller 18 receives the report about the chargingcondition from each power receiver after the power transmission. If itis determined that measured voltages of all the power receivers belongto best efficient voltage regions determined for the respective powerreceivers, the controller 18 determines which power receiver should beused as a base for controlling the power transmission. If any of thepower receivers is selected, the power transmitter 100 adjusts thetransmission power according to the demanded voltage of the selectedpower receiver. Methods of selecting any of the power receivers includeat least one of a method of selecting a power receiver having a highestcurrent reception power from among the plurality of power receivers, amethod of selecting a power receiver having a highest maximum receptionpower from among the plurality of power receivers, and a method ofselecting a power receiver having a highest power usage rate from amongthe plurality of power receivers. If it is determined that there are twoor more power receivers having the high usage rates, the powertransmitter 100 may control the power transmission according to themethod of selecting the power receiver having the highest currentreception power from among the two or more power receivers.

When there is a plurality of power receivers whose measured voltagesbelong to ranges between their respective minimum voltages and therespective reference voltages after the power transmission, thecontroller 18 determines a power control method. The power controlmethods include, for example, a method of adjusting power according tothe demanded power of the power receiver selected from among theplurality of power receivers, and a method of increasing the entireefficiency for the plurality of power receivers.

In an embodiment of the present invention, the power receiver 110further includes a temperature measuring unit 27 for measuring thetemperature out of the rectifier 22 or for measuring a batterytemperature. The controller 25 of the power receiver 110 may set up thereference voltage V_high and the demanded voltage V_opt based oninformation of the temperature measured by the controller 25. Thereference voltage V_high is less than the maximum voltage V_max butgreater than the demanded voltage V_opt. The demanded voltage V-opt isgreater than the minimum voltage V_min but less than the referencevoltage V_high. The reference voltage V_high and the demanded voltageV_opt may be set up by using values determined in advance in the powerreceiver 110 by taking into account a change in hardware design. Forexample, if the reference voltage V_high is 10 V, the demanded voltageV_opt may be set up as 7 V.

The reference voltage V_high and the demanded voltage V_opt are changedaccording to the measured temperature. Specifically, if the measuredtemperature reaches a specific temperature, the power receiver 110 maydecrease the reference voltage V_high and the demanded voltage V_opt.

If the measured temperature is greater than the specific temperature,the reference voltage V_high is decreased to be less than an initialreference voltage V_high informed to the power transmitter 100. Theextent of the decrease may be adjusted in proportion to a differencebetween a current temperature and the specific temperature. For example,if the initial reference voltage V_high is 10 V, the specifictemperature is 45 degrees, the measured temperature is 50 degrees, and amethod of dropping 1 V down for every 5-degree difference is employed,the reference voltage V_high becomes 9 V resulting from the subtractionof 1 V from the initial reference voltage V_high, 10 V. If the measuredtemperature is less than the specific temperature, the reference voltageV_high is increased to be greater than an initial reference voltageV_high. For example, if the specific temperature is 45 degrees, and themeasured temperature is 30 degrees, the reference voltage V_high becomes13 V resulting from the addition of 3V to the initial reference voltageV_high, 10V.

Similarly, if the measured temperature is greater than the specifictemperature, the demanded voltage V_opt may be decreased to an extentthat it becomes less than an initial demanded voltage V_opt. Forexample, if the initial demanded voltage V_opt is 7 V, the specifictemperature is 45 degrees, the measured temperature is 50 degrees, and amethod of decreasing 0.5 V for every 5-degree difference is employed,the changed demanded voltage V_opt becomes 6.5 V resulting from thesubtraction of 0.5 V from 7 V. The initial reference voltage V_high andthe initial demanded voltage V_opt refer to a reference voltage and ademanded voltage, respectively, notified to the power transmitter 100 inthe registration phase.

If the reference voltage V_high and the demanded voltage V_opt becomedifferent from the initial/previous reference voltage V_high and theinitial/previous demanded voltage V_opt, respectively, the powerreceiver 110 notifies the power transmitter 100 of the changed referencevoltage V_high and the changed demanded voltage V_opt in a chargingreport. The changed reference voltage V_high and the changed demandedvoltage V_opt may be periodically/non-periodically reported to the powertransmitter 100.

However, if an increase in temperature for a specific period of timeexceeds the specific temperature, the reference voltage V_high and thedemanded voltage V_opt may be decreased. For example, if the referencevoltage V_high is 7 V and the temperature increases by 5 degrees for 1minute, then the reference voltage V_high may be decreased.

Accordingly, the power transmitter 100 may control the power based oninformation of the reference voltage V_high and demanded voltage V_optof the power receiver 110, and periodically transmitted information ofcurrent temperature of the power receiver 110. Specifically, with theinformation, the power transmitter 100 may provide the power bydetermining that a charging efficiency is low for a power receiver whosetemperature is relatively high, and determining the transmission powerbased on the reference voltage V_high of a power receiver whosetemperature is high. In addition, if it is determined from theinformation of temperature received from the power receiver 110 that thepower receiver 110 exceeds a predetermined temperature threshold, thepower transmitter 100 may stop transmitting the power by transmitting ashut down message to the wireless communication unit 19 to cut off aload switch to the power receiver 110.

However, the power receiver 110 periodically or non-periodically sendsthe power transmitter 100 the reference voltage V_high and the demandedvoltage V_opt determined in the manner described above. In the case ofnon-periodical transmission, the power receiver 110 may transmit theinformation non-periodically when the input voltage Vin demanded by thepower receiver 110 is changed. On the contrary, in the case of periodictransmission, the power receiver 110 may periodically transmit theinformation by inserting the information about the reference voltageV_high and the demanded voltage V_opt to a report frame to betransmitted to the power transmitter 100.

Upon reception of the information about the reference voltage V_high andthe demanded voltage V_opt from the power receiver 110, the powertransmitter 100 may use the received information about the referencevoltage V_high and the demanded voltage V_opt as power transmissioncontrol information. Specifically, establishing ranges of the inputvoltage, according to an embodiment of the present invention, isdescribed in greater detail below with reference to FIG. 2.

Referring to FIG. 2, the minimum voltage V_min indicates a voltage atwhich the charging is cut-off in the charging state, and indicates avoltage from which an under voltage may appear at an output (Vout) or atthe PMIC 24 of the power receiver 110. The minimum voltage may be, e.g.,4.5 V.

The maximum voltage V_max indicates a voltage at which a circuitry on apower transmission line of the power receiver 110 may be damaged. Themaximum voltage may be, e.g., 25 V.

When the range between the minimum voltage V_min and the maximum voltageV_max is 100, the reference voltage V_high indicates a voltage thatdivides the range into two ranges of certain percentages. Thus, therange between the minimum voltage V_min and the maximum voltage V_max isdivided into a first voltage range between the minimum voltage V_min andthe reference voltage V_high, and a second voltage range between thereference voltage V_high and the maximum voltage V_max. The firstvoltage range is defined as an efficient voltage range 220, havinghigher power reception efficiencies than a certain efficiency. Thesecond voltage range is defined as a high voltage range 210, indicatingthat higher power than that required by the power receiver 110 isreceived. An over voltage range 200 is defined above the maximum voltageV_max, and an under voltage range 230 is defined below minimum voltageV_min.

For example, the reference voltage V_high, the reference for determiningthe best efficient voltage range, is calculated as set forth in Equation(1).V _(—high) =V _(—min)+0.3*(V _(—max) −V _(—min))   (1)

In Equation (1), if the minimum voltage V_min is 4.5 V and the maximumvoltage V_max is 25 V, the reference voltage V_high becomes4.5+0.3*(25−4.5), i.e., 10.65 V. A size of each range may be dynamicallychanged according to a device efficiency, such as, for example, theefficiency of the resonator 20, Power Amplifier (PA) efficiency, theefficiency of the rectifier 22, Switched Mode Power Supply (SMPS)efficiency, etc.

Operations of the power receiver 110 are described in greater detailbelow with reference to FIG. 3. The power receiver 110 searches andpairs with the power transmitter 100, registers in the power transmitter100, and starts being charged in a standby mode. After finishing theregistration, the power transmitter 100 may know of the power demandedby the power receiver 110. In this regard, the power receiver 110 sendsthe power transmitter 100 a subscription request frame in theregistration phase to subscribe to a wireless power network controlledby the power transmitter 100. The subscription request frame isrepresented below in Table 1.

TABLE 1 Input Input Typical Typical Frame Protocol Sequence NetworkProduct Voltage Voltage Output Output Type Version Number ID ID Min MaxVoltage Current Request 4 bits 1 byte 1 byte 4 bytes 1 byte 1 byte 1byte 1 byte Join

As shown in Table 1, the subscription request frame includes the minimumvoltage V_min, the maximum voltage V_max, the output voltage Vout, theoutput current Iout, etc. The subscription request frame may furtherinclude the reference voltage V_high to be used a reference fordetermining a relatively better power reception efficiency range ascompared with other ranges, and a demanded voltage V_opt required by thepower receiver 110, according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a case in which information includingthe minimum and maximum voltages are contained in the subscriptionrequest frame received by the power transmitter 100. However, theinformation including the minimum and maximum voltages may be containedin a report frame transmitted by the power receiver 100 to notify thepower transmitter 100 of the power reception condition, after the powerreceiver 110 subscribes to the wireless power network controlled by thepower transmitter 100. Alternatively, the foregoing information may becontained in a response message to be transmitted by the power receiver110 in response to the information request from the power transmitter100, or may be contained in an acknowledgment frame in response to asubscription response frame indicating that the subscription of thepower receiver 110 to the wireless power network has been completed.

Accordingly, the power transmitter 100 performs power transmission bydetermining the range having power reception efficiencies greater thanthe certain efficiency, the magnitude of a varying voltage, the numberof steps, etc., based on the information notified by the power receiver110, and sending a notice frame to inform the power receiver 110 that itoperates in a level-up mode.

The power receiver 110 may periodically measure voltages after receivingthe notice frame. The power receiver 110 may change the referencevoltage V_high and the demanded voltage V_opt based on the informationabout the measured voltage/current and/or the measured temperature.

As such, the power receiver 110 informs the power transmitter 100 of theminimum and maximum voltages receivable at the power receiver 110, thereference voltage to be used as a reference for determining the rangehaving a good charging efficiency, and the demanded voltage required bythe power receiver 110, by sending the power transmitter 100 thesubscription request frame in the registration phase. The powertransmitter 100 then determines the power to be transmitted to the powerreceiver 110 and starts the power transmission. The power receptioncondition is reported from the power receiver 110 according to the powerreception. With the report, the power transmitter 100 may know how toadjust the power to be transmitted to the power receiver 110. The powerreception condition may include a new reference voltage V_highdetermined by the power receiver 110 according to its chargingcondition. The charging condition may be checked by measuring voltage,current, temperature, etc., at the power receiver 110. The referencevoltage V_high may be used for the power transmitter 100 to adjust thebest efficient voltage range for the power receiver 110. Specifically,the power transmitter 100 may adjust the best efficient voltage rangeaccording to a condition of the power receiver 110.

Additionally, the power receiver 100 may contain the demanded voltageV_opt as well as the reference voltage V_high in the power receptioncondition. The demanded voltage V_opt is not actually used for the powertransmitter 100 to determine the transmission power, but is consideredif there is a plurality of power receivers and the amount of powerconsumption in every power receiver is the same. Thus, the powertransmitter 100 may select any of the plurality of power receivers andcontrol the power transmission to fit for the demanded voltage V_opt ofthe selected power receiver.

FIG. 3 is a flowchart illustrating a procedure for changing thereference voltage V_high according to the information about the measuredvoltage/current and/or the measured temperature, according to anembodiment of the present invention.

Referring to FIG. 3, the power receiver 110 measures a voltage, in step300. The power receiver 110 compares the reference voltage V_high,informed by the power transmitter 100, with the measured voltage Vout,in step 305. In step 310, it is determined whether a difference betweenthe reference voltage V_high and the measured voltage Vout is greaterthan a threshold. When the difference between the two voltages isgreater than a threshold, the power receiver 110 changes the referencevoltage V_high, in step 315. The power receiver 110 includes the changedreference voltage V_high in the power condition information, in step320. The power receiver 110 transmits the power condition information tothe power transmitter 100 in a set transmission period, in step 325. Forthis transmission of the power condition information, the report framemay be used.

When the difference between the two voltages is not greater than thethreshold in step 310, the reference voltage V_high may still bechanged. In an embodiment of the present invention, the fact that anamount of power demanded by the power receiver 110 varies according to,e.g., a difference in temperature is taken into consideration. Thus, if,in step 310, the difference between the two voltages is not greater thanthe threshold, the power receiver 110 measures a temperature, in step330. In step 335, the power receiver 110 determines whether thetemperature is greater than a threshold temperature for a certain periodof time, in step 335. For example, if the reference voltage is 7 V andthe temperature increases 5 degrees for 1 minute, it is desirable forthe reference voltage V_high to be decreased due to concerns aboutoverheating. If the temperature is kept greater than the thresholdtemperature for a certain period of time, the reference voltage V_highis changed, in step 315. If the temperature is not greater than thethreshold temperature, the power receiver 110 sends the power conditioninformation in the set transmission period, in step 325.

FIG. 4 is a flowchart illustrating a procedure of changing the referencevoltage V_high and the demanded voltage V_opt according to the measuredtemperature at the power receiver 110, according to another embodimentof the present invention.

The power receiver 110 measures the temperature, in step 400. The powerreceiver 110 determines whether the measured temperature is greater thanor equal to the threshold temperature, in step 405. If the measuredtemperature is greater than or equal to the threshold temperature, thepower receiver 110 decreases the reference voltage V_high and thedemanded voltage V_opt, in step 410. On the contrary, if the measuredtemperature is less than the threshold temperature, the power receiver110 increases the reference voltage V_high and the demanded voltageV_opt, in step 415. The extent of the decrease or increase is determinedin proportion to a difference between the currently measured temperatureand the threshold temperature. For example, if the measured temperatureis greater than or equal to the threshold temperature, the powerreceiver 110 determines that the temperature has increased due to thehigh transmission power from the power transmitter 100 and thus,decreases the reference voltage V_high, expecting the transmission powerto be decreased. Once the reference voltage V_high and the demandedvoltage V_opt are determined, the power receiver 110 includes thereference voltage V_high and the demanded voltage V_opt in the powercondition information, in step 420, and transmits the power conditioninformation to the power transmitter 100, in step 425. The report frameis used to transmit the power condition information.

By varying the reference voltage V_high according to the condition ofthe power receiver 110, the power transmitter 100 adjusts the bestefficient voltage range to suit the condition of the power receiver 110.Furthermore, when the power receiver 110 suffers from, e.g., heating, itis possible for the power receiver 110 to decrease the charging voltagesupplied by the power transmitter 100.

Operational steps between the power transmitter 100 and the powerreceiver 110, in which the power receiver 110 determines the minimumvoltage V_min, the maximum voltage V_max, the reference voltage V_high,and the demanded voltage V_opt and transmits them to the powertransmitter 100, are described with reference to FIG. 5.

Referring to FIG. 5, in step 500, the power transmitter 100 receives thesubscription request from the power receiver 110. The power transmitter100 transmits the subscription reply, in step 505, completing aregistration phase 550. The subscription request includes an initialreference voltage V_high and an initial demanded voltage V_opt, as wellas the maximum voltage V_max and the minimum voltage V_min determined bythe power receiver 110. The initial reference voltage V_high and theinitial demanded voltage V_opt are determined in advance by the powerreceiver 110 by considering its charging capacity, the dimension of itsresonator, etc.

Thus, the power transmitter 100 may determine the best efficient voltagerange by using the initial reference voltage V_high, in step 507.Specifically, by knowing the initial reference voltage V_high, the powertransmitter 100 may determine not only the efficient voltage range 220between the minimum voltage V_min and the reference voltage V_high, butalso the over voltage range 200, the high voltage range 210 between themaximum voltage V_max and the reference voltage V_high, and the undervoltage range 230.

Accordingly, the power transmitter 100 may know of the range having goodcharging efficiencies for the power receiver 110 based on the referencevoltage V_high, and know of an optimum input voltage required by thepower receiver 110 based on the demanded voltage V_opt. The referencevoltage V_high is used by the power transmitter 100 to determine thebest efficient voltage range, and the power transmitter 100 adjusts thetransmission power to be increased or decreased by determining whichrange the voltage measured at the power receiver 110 receiving thetransmission power belongs to while charging the power receiver 110.Thus, the reference voltage V_high is used by the power transmitter 100to control the direct power transmission. However, the demanded voltageV_opt is only used to determine how much voltage is demanded by thepower receiver 110. If there is a plurality of power receivers in thecharging area, the power transmitter 100 controls the power transmissionso as not to deteriorate the transmission efficiency for each powerreceiver 110, rather than simultaneously transmit respective power thatcorresponds to respective demanded voltages V_opt to all of the powerreceivers. However, if amounts of power consumption at the plurality ofpower receivers 100 are the same, the power transmitter 100 controls thepower transmission to suit the demanded voltage V_opt of one of theplurality of power receivers.

After transmission of the subscription reply and setting the efficientvoltage range, the power transmitter 100 transmits a start chargingcommand, in step 515, when the power transmitter 100 has enough power tocharge the standby power receiver 110. By sending the start chargingcommand, a charging phase 560 begins. At the same time the startcharging command is sent, the power transmitter 100 supplies thetransmission power. As the charging begins, the power receiver 110measures its power reception condition and temperature, in step 520, andtransmits a charging report that includes the power conditioninformation, in step 525. The power transmitter 100 adjusts thetransmission power by using the power condition information, in step530.

Specifically, the power transmitter 100 determines if a measured voltageincluded in the power condition information belongs to the bestefficient voltage range. If the measured voltage is out of the bestefficient voltage range but belongs to the over reference voltage range,the power transmitter 100 reduces the transmission power. If themeasured voltage belongs to the over maximum voltage range, the powertransmitter 100 stops transmitting power by cutting off the transmissionpower. If the measured voltage belongs to the under minimum voltagerange, the power transmitter 100 increases the transmission power. Also,during the charging in the charging phase 560, the power receiver 110measures the power reception condition and the temperature, in step 535,and periodically/non-periodically transmits the charging reportincluding the power condition information, in step 540.

The report frame is used to transmit the charging report. For example,the report frame may include not only the information about the outputvoltage Vout, the output current Iout, and the input voltage Vin, butalso the temperature information, information about the referencevoltage V_high, the demanded voltage V_opt, and Power Control Preference(PCP), as the power condition information. The PCP refers to a powercontrol method required of the power transmitter 100 by the powerreceiver 110. The PCP includes a method of matching the transmissionpower from the power transmitter 100 to a power receiver having thehighest current reception power, or a method of increasing the entireefficiency, in determining the transmission power at the powertransmitter 100. Such power control methods are described in greaterdetail below with reference to FIG. 6.

Meanwhile, upon reception of the report frame, the power transmitter 100adjusts the best efficient voltage range by using the new referencevoltage V_high included in the received report frame. As the bestefficient voltage range is adjusted, the over reference voltage range ischanged accordingly. Subsequently, in step 545, the power transmitter100 adjusts the transmission power by using the power conditioninformation of the report frame. Specifically, as in step 530, the powertransmitter 100 adjusts the transmission power by, e.g., decreasing orincreasing the transmission power according to the range the measuredvoltage belongs to. In this manner, the power transmitter 100 may catchthe power condition of the power receiver 110 based on the chargingreport delivered during the charging, and may adaptively adjust thetransmission power by reflecting the charging condition of the powerreceiver 110.

A plurality of power receivers may be disposed in a charging area of thesingle power transmitter 100. Furthermore, if a voltage measured by eachpower receiver belongs to the best efficient voltage range of the eachpower receiver, the power transmitter 100 has to determine which powerreceiver or what reference voltage should be used as a base to adjustthe transmission power. The reference voltage V_high was already used todetermine the best efficient voltage range, so in this case, a demandedvoltage V_opt of each power receiver may be used.

A method of setting the reference is defined as the power controlmethod, including the PCP such as, for example, a method of suiting apower receiver having the highest current reception power, a method ofincreasing the entire efficiency, etc. In addition to the foregoingpower control methods, the power transmitter 100 tracks the power tocontrol the transmission power as described below.

There is a method of suiting a power receiver having the highest currentreception power among the plurality of power receivers. In this method,the power transmitter 100 may track the power to maximize the efficiencyof a power receiver having the highest power consumption from among thepower receivers. For example, if measured voltages included in thecharging reports sent by a first power receiver and a second powerreceiver fall under the best efficient voltage range known to the powertransmitter 100, the power transmitter 100 calculates respective currentreception power by using the respective output voltages Vout and theoutput currents Tout included in charging report. Specifically, chargedpower in the power receiver may be calculated by multiplying the outputvoltage Vout and the output current Tout included in the chargingreport, and accordingly, the power transmitter 100 may know which powerreceiver is currently consuming the highest power out of thetransmission power supplied by the power transmitter 100, and maycontrol the transmission power to suit the power receiver consuming thehighest power.

When the output voltage Vout and the output current Tout informed by thefirst power receiver in the registration phase are 5 V and 20 mA,respectively, the power transmitter 100 may calculate the highestchargeable capacity, i.e., the highest reception power P to be 100 W.Furthermore, when the output voltage Vout and the output current Toutinformed by the second power receiver in the registration phase are 5 Vand 10 mA, respectively, the power transmitter 100 may calculate thehighest chargeable capacity, i.e., the highest reception power P to be50 W. After these initial calculations, when the output voltage Vout andthe output current Tout included in the power reception condition withinthe charging report sent by the first power receiver are 5 V and 12 mA,respectively, the current reception power P may be 60 W, and when theoutput voltage Vout and the output current Tout included in the powerreception condition of the second power receiver are 5 V and 10 mA,respectively, the current reception power P may be 50 W. Thus, the powertransmitter 100 may be aware that the first power receiver has 100 W ofmaximum chargeable capacity but actually has consumed only 60 W, whilethe second power receiver has 50 W of maximum chargeable capacity butactually has consumed 50 W.

The power transmitter 100 adjusts the transmission power to suit thefirst power receiver having more power consumption, i.e., having thehigher current reception power. Specifically, the power transmitter 100selects the first power receiver that is currently consuming the highestpower, and determines a transmission power to match the demanded voltageV_opt to the input voltage Vin of the selected first power receiver. Forexample, the power transmitter 100 compares the demanded voltage V_optand the input voltage Vin of the first power receiver. If the demandedvoltage V_opt is greater than the input voltage Vin, the powertransmitter 100 increases the transmission power. If the demandedvoltage V_opt is less than the input voltage Vin, the transmission poweris decreased. Alternatively, the power transmitter 100 may check the PCPof the selected first power receiver, and may determine the transmissionpower in a way defined by the checked power control method. Thetransmission power may be determined depending on whether the PCP of thefirst power receiver is the method of suiting the power receiver havingthe highest current reception power, or the method of increasing theentire efficiency.

There is another method to increasing the entire efficiency, accordingto which the power transmitter 100 may track the power to maximize theefficiency of the entire power transmission system, i.e., the efficiencyof the power transmitter 100 and the power receivers, after receivinginformation about the demanded voltage V_opt from the plurality of powerreceivers. For example, assuming the current reception power P of thefirst power receiver is 60 W, calculated based on information containedin the power reception condition in the charging report of the firstpower receiver, and the current reception power P of the second powerreceiver is 50 W, calculated based on information contained in the powerreception condition in the charging report of the second power receiver,the entire efficiency may be obtained in accordance with Equation (2)below.Entire Efficiency (%)=(Power of First Power Receiver (Prx1)+Power ofSecond Power Receiver (Prx2))/Power of Power Transmitter (Ptx)   (2)

The power transmitter 100 may determine the transmission power accordingto the highest entire efficiency among entire efficiencies repeatedlycalculated by the equation (2). For example, if the previous entireefficiency is higher than the current entire efficiency, the powertransmitter 100 maintains the transmission power determined at theprevious efficiency. if the previous entire efficiency is lower than thecurrent entire efficiency, the power transmitter 100 may adjust thetransmission power.

The power transmitter 100 may track the power to suit the power receiverhaving highest power usage rate. The power usage rate refers to a ratioof the demanded power to the reception power. Specifically, the powertransmitter 100 may select a power receiver having the highest ratio ofcurrent power to maximum reception power from among the plurality ofpower receivers, and then track the power in a power control methodincluded in the PCP received from the selected power receiver.Alternatively, the power transmitter 100 may control the transmissionpower to match the demanded voltage V_opt of the selected power receiverto the input voltage Vin reported from the selected power receiver.

For example, assuming the first power receiver has 100 W of the maximumchargeable capacity, i.e., the maximum reception power, and actuallyconsumed only 60 W resulting in 60 W/100 W=60% of the power usage rate,while the second power receiver has 50 W of the maximum chargeablecapacity and actually consumed 50 W, resulting in 50 W/50 W=100% of thepower usage rate, the power transmitter 100 tracks the power to suit thesecond power receiver having the higher power usage rate. Specifically,the power transmitter 100 determines the transmission power to match thedesired voltage V_opt of the second power receiver to the input voltageVin reported by the second power receiver. Alternatively, the powertransmitter 100 may refer to the PCP of the second power receiver andperform the power control in a method defined by the PCP. Adjustment ofthe transmission power to suit the second power receiver having betterreception ratio compared to the first power receiver also leads to achange in the measured voltage of the first power receiver.

Referring to FIG. 6, when adjusting the transmission power with respectto the second power receiver and increasing the transmission power tothe second power receiver, the voltage measured at the first powerreceiver also increases accordingly. For example, as in FIG. 6, if thetransmission power is increased because the measured voltage at thesecond power receiver belongs to the under minimum voltage range 230,the measured voltage at the first power receiver may belong to the overreference voltage range 210. In this case, the transmission power may bedetermined to increase power reception efficiencies of the first andsecond power receivers, e.g., with the adjustment of increasing ordecreasing the transmission power based on the charging report receivedduring the charging.

The power transmitter 100 may track the power to suit the power receiverhaving the highest reception power among the plurality of powerreceivers. For example, in the case of the second power receiver, themaximum reception power is calculated by the power transmitter 100 to be10 W, 5 W higher than the maximum reception power of the first powerreceiver. Thus, the transmission power may be adjusted to suit thesecond power receiver. Accordingly, the transmission power may bedetermined to match the demanded voltage V_opt of the second powerreceiver to the input voltage Vin reported by the second power receiver,or the PCP of the second power receiver is referred to and the powercontrol may be performed in a method defined by the PCP.

If there are two or more power receivers having the same power usagerates, the power transmitter 100 may select one having a higher currentreception power, and track the power to suit the selected powerreceiver. For example, if the second power receiver is selected, thetransmission power may be determined to match the demanded voltage V_optof the second power receiver to the input voltage Vin reported by thesecond power receiver, or the transmission power may be determinedaccording to a power transmission control method included in the PCP ofthe second power receiver.

As described above, if each power receiver provides the maximum voltage,the minimum voltage, the reference voltage, and the demanded voltage inthe registration phase, the power transmitter 100 has to determine whichpower receiver or what reference should be used as a base to control thetransmission power. Embodiments of the present invention propose usingthe above-described methods.

Accordingly, the power transmitter 10 adjusts the transmission poweraccording to the basis to which all of conditions, such as, for example,the power usage rate, the current reception power, the maximum receptionpower, and the entire efficiency, are applied. When controlling thepower based on the efficiency, the power transmitter 100 increases (ordecreases) the transmission power and calculates the efficiency by usinginformation included in the power reception condition received from thepower receiver. If the efficiency gets better, compared to theefficiency in the step prior to changing the transmission power, thepower transmitter 100 may keep the transmission power the same orincrease (or decrease) the transmission power. If the efficiency getsworse again in this procedure, the power transmitter 100 may keep thechanged transmission power the same or decreases (or increases) thetransmission power. Alternatively, the power transmitter 100 controlsthe transmission power by selecting one of a plurality of powerreceivers based on any of the power usage rate, the current receptionpower, and the maximum reception power, comparing the demanded voltageand the input voltage of the selected power receiver, increasing thetransmission power if the demanded voltage is larger than the inputvoltage, and decreasing the transmission power if the demanded voltageis less than the input voltage.

The foregoing procedure is described in greater detail below withreference to FIG. 7. FIG. 7 is a diagram illustrating a method ofclassifying power control methods, according to an embodiment of thepresent invention.

The power transmission control methods are largely classified into twogroups based on the number of power receivers used in the power control.In one of the two cases that a single power receiver is selected, it mayfurther be classified based on whether to apply any one of conditions ofreception power, reference reception power and power usage rate, or toapply two or more of these conditions.

Specifically, the power transmitter 100 performs power transmission toeach power receiver after receiving from at least one power receiver theminimum and maximum voltages receivable at the power receiver, thereference voltage used to divide the range between the minimum andmaximum voltages into predetermined portions, and the demanded voltagerequired by the power receiver. In return, the power transmitter 100receives from each power receiver a report of the power receptioncondition that includes a measured voltage at the power receiver. Thepower transmitter 100 determines which of the divided portions (orranges) the measured voltage included in the report belongs to wheneverreceiving the report. The reference voltage may be changed according to,e.g., a temperature, and thus the reference voltage included in thereport about the power reception condition may also be changed. Voltageranges of the power receiver may also be changed. Thus, the powertransmitter 100 determines which of the voltage ranges, of each powerreceiver sending the report, the measured voltage included in the reportbelongs to.

All of the plurality of power receivers may have their measured voltagesbelonging to their optimum voltage ranges, respectively. In this case,the power transmitter 100 has to determine what reference should beapplied to track the power, i.e., which power transmission controlmethod should be applied.

Referring to FIG. 7, a power transmission control method 700 may belargely classified into two groups: a method 705 of using information ofthe plurality of power receivers, and a method 710 of using informationof one power receiver selected from among the plurality of powerreceivers.

When selecting the method 705, using the information of the plurality ofpower receivers, the power transmitter 100 increases the entireefficiency, in step 715. The efficiency is increased after calculatingthe efficiency to be the ratio of the transmission power to thereception power of all the power receivers as in Equation (2), in step720.

When selecting the method 710, using the information of one selectedpower receiver, the method 710 may be classified into a case 725 ofapplying a single condition and a case 730 of applying a plurality ofconditions. The conditions may include the reception power, thereference reception power, and the power usage ratio.

For example, when the plurality of power receivers report their measuredvoltages belonging to best efficient voltage regions, the powertransmitter 100 may select any of a power receiver having the highestreception power 735, a power receiver having the highest referencereception power 740, and a power receiver having the highest power usagerate 745 among the plurality of receivers. Similarly, in the case ofapplying the plurality of conditions, the power transmitter 100 mayselect a power receiver having higher reception power and power usagerate 750. In this manner, the power transmitter 100 may select any ofthe power usage rate and reception power 755, the reference receptionpower and power usage rate 760, the power usage rate and referencereception power 765, the reference reception power and reception power770, and the reception power and reference reception power 775.

When any power receiver is selected under the foregoing condition, thepower transmitter 100 performs the power transmission control, i.e.,power adjustment to suit the demanded voltage of the selected powerreceiver, or performs the power transmission control according to theestablished PCP of the selected power receiver. The PCP is a powercontrol method requested of the power transmitter 100 by the selectedpower receiver, and for this, either a method of adjusting the power tosuit the demanded voltage of the selected power receiver, or a method ofincreasing the entire efficiency for the plurality of power receiversmay be set up, in step 780.

According to the present invention, the demanded power may be determinedand notified to the power transmitter 100 by taking into account variouscharging conditions, such as, for example, the power receiver'scharacteristics, the charging condition, and the difference intemperature, thereby allowing for the power transmitter to control theefficient power transmission. Furthermore, by enabling the powerreceiver and the power transmitter to check each other via wirelesscommunication, incorrect power transmission may be prevented andreliability of the multiple power transmission system may be secured.

While the invention has been shown and described with reference tocertain embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the following claims.

What is claimed is:
 1. A method of controlling power transmission in apower transmitter, the method comprising: receiving, from a plurality ofpower receivers, voltage information required by the plurality of powerreceivers, wherein the voltage information includes a minimum voltage, areference voltage that is greater than the minimum voltage, and ademanded voltage; transmitting power to the plurality of powerreceivers; receiving, from the plurality of power receivers, a reportabout a power reception condition while transmitting the power, whereinthe report includes a measured voltage at the plurality of powerreceivers; selecting one of the plurality of power receivers; andadjusting an amount of the power by minimizing a difference between thedemanded voltage and the measured voltage of the selected powerreceiver.
 2. The method of claim 1, further comprising stopping thepower transmission, if the measured voltage is greater than apredetermined value.
 3. The method of claim 1, wherein selecting one ofthe plurality of power receivers comprises selecting a power receiverwith a highest power usage rate among the plurality of power receivers.4. The method of claim 1, wherein selecting one of the power receiverscomprises selecting a power receiver with a highest reference receptionpower among the plurality of power receivers.
 5. The method of claim 1,further comprising adjusting the amount of the power to increase anentire efficiency for the plurality of power receivers, when themeasured voltage at each of the plurality of power receivers is betweenthe minimum voltage and the reference voltage.
 6. The method of claim 1,wherein the minimum voltage, the reference voltage, and the demandedvoltage are included in a request frame sent by at least one powerreceiver to join a wireless power network hosted by the powertransmitter or a report frame sent by the at least one power receiver toannounce the power reception condition after the at least one powerreceiver joins the wireless power network.
 7. The method of claim 1,wherein the report about the power reception condition includes at leastone of a voltage at a charger of at least one power receiver, a voltagemeasured at a rectifier output of the at least one power receiver, and acurrent measured at the at least one power receiver during powerreception, a changed reference voltage, a changed demanded voltage, anda measured temperature.
 8. A power transmitter for controlling powertransmission, the power transmitter comprising: a resonator; a powersupply; a wireless communication unit configured to receive, from aplurality of power receivers, voltage information required by theplurality of power receivers, wherein the voltage information includes aminimum voltage, a reference voltage that is greater than the minimumvoltage, and a demanded voltage, and to receive, from the plurality ofpower receivers, a report about a power reception condition whiletransmitting power, wherein the report includes a measured voltage atthe plurality of power receivers; and a controller configured to:control the power supply to transmit the power to the plurality of powerreceivers through the resonator; select one of the plurality of powerreceivers; and adjust an amount of the power by minimizing a differencebetween the demanded voltage and the measured voltage of the selectedpower receiver.
 9. The power transmitter of claim 8, wherein thecontroller is further configured to stop the power transmission, if themeasured voltage is greater than a predetermined value.
 10. The powertransmitter of claim 8, wherein the controller is further configured toselect a power receiver with a highest power usage rate among theplurality of power receivers.
 11. The power transmitter of claim 8,wherein the controller is further configured to select a power receiverwith a highest reference reception power among the plurality of powerreceivers.
 12. The power transmitter of claim 8, wherein the controlleris further configured to adjust the amount of the power to increase anentire efficiency for the plurality of power receivers if the measuredvoltage at each of the plurality of power receivers is between theminimum voltage and the reference voltage.
 13. The power transmitter ofclaim 8, wherein the minimum voltage, the reference voltage, and thedemanded voltage are included in a request frame sent by at least onepower receiver to join a wireless power network hosted by the powertransmitter or a report frame sent by the at least one power receiver toannounce the power reception condition after the at least one powerreceiver joins the wireless power network.
 14. The power transmitter ofclaim 8, wherein the report about the power reception condition includesat least one of a voltage at a charger of at least one power receiver, avoltage measured at a rectifier output of the at least one powerreceiver, and a current measured at the at least one power receiverduring power reception, a changed reference voltage, a changed demandedvoltage, and a measured temperature.